(APSS). Compensatory imbalance in sodium and water homeostasis usually becomes clinically apparent with onset of portal hypertension associated with a subnormal albumin concentration. Ascitic effusion associated with hepatic disease is usually characterized as a modified or pure transudate (serum albumin <1.8 g/dL).

The first step in control of ascites is dietary sodium restriction. An intake of ≤100 mg/100 kcal (25 mg/kg/day; <0.1% dry matter basis in food) is recommended. However, sodium-restricted diets alone are often insufficient and too slow in onset for efficient management. Thus, diuretics are usually recommended. Diuretic therapy should slowly reduce ascites without causing dehydration, metabolic alkalosis, or hypokalemia. Reducing ascites by ≤1.0–1.5% of total body wt/day is recommended. Dual therapy with furosemide (1–2 mg/kg, PO, bid) and spironolactone (loading dose 2–4 mg/kg × 2–3 doses, then 1–2 mg/kg, PO, bid) is initially recommended. Reevaluation every 7–10 days allows for careful upward titration of diuretic dosages. Combining a loop diuretic with spironolactone reduces risk of iatrogenic hypokalemia.

If ascites is slow to resolve, measuring the urinary fractional excretion of sodium can help determine whether dietary restriction and diuretic dosing are adequate. If ascites causes tense abdominal distention, compromising ventilation, appetite, and patient comfort, a therapeutic abdominocentesis is recommended. Fluid administration (hetastarch) reduces risk of post-diuresis circulatory dysfunction developing ~12-hr after effusion removal when body fluids undergo re-equilibration (hypotension, worsening hypoalbuminemia). However, Hetastarch infusion increases risk of bleeding because of reduced platelet aggregation. As little ascitic fluid as possible should be removed to keep the animal comfortable. Reducing abdominal pressure increases renal perfusion and cardiac output and improves response to diuretic therapy. In many cases, once fluid is mobilized, diuretics can be used intermittently as long as a attention to dietary sodium restriction is maintained.